U.S. patent number 10,320,026 [Application Number 15/521,272] was granted by the patent office on 2019-06-11 for electrode for secondary battery and secondary battery using same.
This patent grant is currently assigned to NEC Corporation. The grantee listed for this patent is NEC Corporation. Invention is credited to Takeshi Azami.
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United States Patent |
10,320,026 |
Azami |
June 11, 2019 |
Electrode for secondary battery and secondary battery using
same
Abstract
A secondary battery which is highly safe even when it becomes in
excessively high-temperature conditions and is excellent in cycle
characteristics, and an electrode for a secondary battery are
provided. The present invention relates to an electrode for a
secondary battery comprising a maleimide compound and a conductive
agent, wherein the conductive agent comprises at least one selected
from carbon nanotube and carbon nanohorns.
Inventors: |
Azami; Takeshi (Tokyo,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
NEC Corporation |
Tokyo |
N/A |
JP |
|
|
Assignee: |
NEC Corporation (Tokyo,
JP)
|
Family
ID: |
55760850 |
Appl.
No.: |
15/521,272 |
Filed: |
October 16, 2015 |
PCT
Filed: |
October 16, 2015 |
PCT No.: |
PCT/JP2015/079352 |
371(c)(1),(2),(4) Date: |
April 21, 2017 |
PCT
Pub. No.: |
WO2016/063813 |
PCT
Pub. Date: |
April 28, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170309948 A1 |
Oct 26, 2017 |
|
Foreign Application Priority Data
|
|
|
|
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Oct 21, 2014 [JP] |
|
|
2014-214820 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M
4/625 (20130101); H01M 4/13 (20130101); H01M
4/62 (20130101); H01M 10/05 (20130101); H01M
4/139 (20130101); H01M 10/052 (20130101); H01M
2004/028 (20130101); Y02E 60/10 (20130101) |
Current International
Class: |
H01M
10/05 (20100101); H01M 10/052 (20100101); H01M
4/13 (20100101); H01M 4/62 (20060101); H01M
4/02 (20060101); H01M 4/139 (20100101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
2003-77476 |
|
Mar 2003 |
|
JP |
|
2009-155593 |
|
Jul 2009 |
|
JP |
|
2010-157512 |
|
Jul 2010 |
|
JP |
|
2012-134125 |
|
Jul 2012 |
|
JP |
|
2012-134149 |
|
Jul 2012 |
|
JP |
|
2012-138359 |
|
Jul 2012 |
|
JP |
|
2012-221672 |
|
Nov 2012 |
|
JP |
|
2012-243696 |
|
Dec 2012 |
|
JP |
|
WO 2013/150937 |
|
Oct 2013 |
|
WO |
|
WO 2015/029525 |
|
Mar 2015 |
|
WO |
|
Other References
Machine translation of JP 2009-155593, published on Jul. 16, 2009
(Year: 2009). cited by examiner .
Machine translation of JP 2010-024455, published on Feb. 4, 2010
(Year: 2010). cited by examiner .
International Search Report and Written Opinion dated Nov. 17,
2015, in corresponding PCT International Application. cited by
applicant.
|
Primary Examiner: Eoff; Anca
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
Claims
The invention claimed is:
1. An electrode for a secondary battery comprising a maleimide
compound, a conductive agent and an electrode active material,
wherein the maleimide compound is a maleimide resin compound
comprising a repeating unit comprising a maleimide monomer residue
and a dione compound residue, the conductive agent comprises at
least one selected from carbon nanotubes and carbon nanohorns, and
a ratio of a coverage of the maleimide compound on the electrode
active material to a coverage of the conductive agent on the
electrode active material is 0.15 to 2.
2. The secondary battery electrode according to claim 1, wherein
the maleimide compound has two or more maleimide groups.
3. The secondary battery electrode according to claim 1, wherein
the maleimide compound comprises a polymer which is a reaction
product of a bismaleimide and a barbituric acid.
4. The secondary battery electrode according to claim 1, wherein
the conductive agent comprises a carbon nanotube.
5. The secondary battery electrode according to claim 4, wherein
the average D/G ratio according to Raman spectroscopic measurement
of the carbon nanotube is 0.2 to 1.2.
6. The secondary battery electrode according to claim 4, wherein
the aspect ratio of the carbon nanotube is 200 to 900.
7. The secondary battery electrode according to claim 1, wherein
the conductive agent further comprises carbon black.
8. A secondary battery comprising the secondary battery electrode
according to claim 1.
9. The secondary battery according to claim 8 comprising the
secondary battery electrode as a positive electrode.
10. An assembled battery comprising the secondary battery according
to claim 8.
11. The secondary battery electrode according to claim 1, wherein
the ratio is 0.15 to 1.
12. The secondary battery electrode according to claim 1, wherein
an amount of the maleimide compound is 0.1 to 1.0 wt % of the
electrode active material and an amount of the conductive agent is
0.5 to 4.5 wt % of the electrode active material.
13. The secondary battery electrode according to claim 1, wherein
the maleimide compound is a maleimide resin compound prepared by
reacting a maleimide monomer and a dione compound in a solvent
containing a Bronsted base.
14. The secondary battery electrode according to claim 1, wherein
an amount of the maleimide compound is 0.1 wt % or less of the
electrode active material.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
This application is a National Stage Entry of International
Application No. PCT/JP2015/079352, filed Oct. 16, 2015, which
claims priority from Japanese Patent Application No. 2014-214820,
filed Oct. 21, 2014. The entire contents of the above-referenced
applications are expressly incorporated herein by reference.
TECHNICAL FIELD
The present invention relates a secondary battery electrode, a
secondary battery using the same, and a method for manufacturing
the same.
BACKGROUND ART
Secondary batteries such as lithium ion secondary batteries have
advantages such as high energy density, small self-discharge,
excellent long-term reliability and the like, and therefore they
have been put into practical use in notebook-type personal
computers and mobile phones. More recently, the development of the
high performance secondary battery having further improved capacity
and energy density is demanded due to, in addition to the trend of
high functionality of electronic equipment, the expansion of market
of motor driven vehicles such as electric vehicles and hybrid
vehicles and the acceleration of the development of domestic and
industrial power storage systems.
However, in the batteries having high capacity and high energy
density, the temperature rise of the battery is liable to occur
when an external shock is applied or they are in overcharged state.
In particular, in a battery containing a positive electrode active
material having high capacity and high energy density, for example
compounds of layered rock-salt structure containing nickel or
cobalt, there is a tendency that energy released during thermal
decomposition is increased, and therefore, the consideration to
safety is furthermore needed.
To increase the safety of batteries of high energy density, there
have been conducted various studies so far. In particular, with
respect to the heat generation in batteries, there have been
conducted studies on cut off mechanism to stop the function of the
battery when the battery temperature rises. For example, Patent
Document 1 discloses a lithium battery comprising a positive
electrode plate, a negative electrode plate and a heat insulating
layer disposed on the charge-discharge surface of the electrode
plates, the lithium battery being capable of reducing the
electrical conductivity when the temperature of the lithium battery
increases. Patent Document 2 discloses a lithium battery having a
thermal actuation protective film formed on the material surface of
a positive electrode plate or a negative electrode plate, in which
if the temperature of the lithium battery rises to the thermal
actuation temperature of the thermally actuation protective film,
the thermal actuation protective film undergoes a cross-linking
reaction to prevent thermal runaway. Patent Document 3 discloses a
lithium battery comprising an electrode plate formed of a plurality
of the electrode material layer and comprising a thermally
activatable material in at least one of these electrode material
layers, in which when the temperature of the lithium battery rises,
the thermally activatable material is activated to undergo
cross-linking reaction, thereby reducing the electrical
conductivity. In the batteries disclosed in these Patent Documents
1, 2 and 3, the heat insulating layer (Patent Document 1), the
thermal actuation protection film (Patent Document 2) and the
electrode material layer (Patent Document 3), respectively,
comprises a nitrogen-containing polymer formed by the reaction of
bismaleimide monomer and barbituric acid, and the conductivity of
the batteries are lowered by such a mechanism that when the
temperature of the batteries rises, the polymer is converted into a
cross-linked polymer which inhibits the diffusion of lithium ions.
In other words, these batteries provide a shutdown function to
batteries by using heat-reactivity of maleimide group of the
polymer.
CITATION LIST
Patent Document
Patent Document 1: Japanese Patent Laid-Open No. 2012-138359
Patent Document 2: Japanese Patent Laid-Open No. 2010-157512
Patent Document 3: Japanese Patent Laid-Open No. 2012-134149
SUMMARY OF INVENTION
Technical Problem
However, the use of an electrode containing a resin compound having
a maleimide group has a problem that the resistance of the
secondary battery becomes higher, and therefore sufficient cycle
characteristics is not obtained.
Solution to Problem
The present invention relates to the following items.
An electrode for a secondary battery comprising a maleimide
compound and a conductive agent, wherein
the conductive agent comprises at least one selected from carbon
nanotubes and carbon nanohorns.
Advantageous Effect of Invention
According to the present invention, there is provided a secondary
battery which is highly safe even when it becomes in excessively
high temperature conditions and is excellent in cycle
characteristics.
BRIEF DESCRIPTION OF DRAWING
FIG. 1 shows an example of a cross-sectional structure of a
secondary battery of the present embodiment.
FIG. 2 shows a schematic cross-sectional view of the structure of a
stack-laminate type secondary battery according to an embodiment of
the present invention.
FIG. 3 shows an exploded perspective view showing a basic structure
of a film package battery.
FIG. 4 shows a schematic cross-sectional view showing the
cross-section of the battery of FIG. 3.
DESCRIPTION OF EMBODIMENTS
<Electrode>
The secondary battery electrode (may be simply referred to as
"electrode") of the present embodiment comprises a maleimide
compound, and at least one selected from carbon nanotubes and
carbon nanohorns as a conductive agent. In this specification, the
conductive agent selected from carbon nanotubes and carbon
nanohorns is referred to as "first conductive agent".
The electrode of the present embodiment comprises a maleimide
compound and a first conductive agent, and preferably, the surface
of the electrode active material is covered with the maleimide
compound and the first conductive agent. An electrode is formed by
forming, on a current collector, an electrode active material layer
containing an electrode active material covered with the maleimide
compound and the first conductive agent, and an electrode binder.
The electrode comprising the maleimide compound and the first
conductive agent can be either one or both of a positive electrode
and a negative electrode, but is preferably at least a positive
electrode. A lithium-ion secondary battery using the electrode of
the present embodiment (hereinafter, may be referred to as
"battery") has excellent cycle characteristics, and also excellent
in safety when the lithium ion secondary battery is brought to a
high temperature by overcharge or the like.
In the electrode of the present embodiment, when the temperature of
the lithium-ion secondary battery rises to high temperature (for
example, 80.degree. C. or higher, preferably 80 to 280.degree. C.),
since the reaction of maleimide groups in the maleimide compound
takes place to form cross-linking, diffusion and conduction of
lithium ions are blocked (shut down), and therefore, the thermal
runaway of the battery is prevented. On the other hand, whereas
there is a problem that the use of maleimide compound lowers a
conductivity to increase the resistance of the secondary battery,
the electrode of the present embodiment suppresses the decrease in
conductivity by containing the first conductive agent, and a
battery using this electrode is excellent in cycle characteristics.
The present inventor has found that the use of the first conductive
agent as the conductive agent in an electrode comprising a
maleimide compound results in a battery particularly excellent in
cycle characteristics and safety. Firstly, maleimide compound
contained in the electrode of the present embodiment and the first
conductive agent are described.
(Maleimide Compound)
Maleimide compounds is not particularly limited as long as it is a
compound having at least one maleimide group in a molecule, but it
is preferably a compound having two or more maleimide groups, and
more preferably a compound having 3 or more maleimide groups. If
the number of maleimide groups in a molecule is larger, it is easy
to form a network by cross-linking when temperature of the
secondary battery is elevated.
Examples of maleimide compound include maleimide monomers having
maleimide group(s), maleimide resin compounds obtained by
polymerizing maleimide monomers and the like, but the maleimide
compound preferably comprises a maleimide resin compound. The
maleimide resin compounds may be homopolymers or copolymers.
Examples of the maleimide monomer include monomaleimide monomers
that is used in the preparation of maleimide resin compounds
described in detail below, bismaleimide monomers, trismaleimide
monomers and multi-maleimide monomers of tetra- or
more-functionality.
As a preferred embodiment of the maleimide resin compound,
description will be made to hyperbranched polymers having a highly
branched structure. Since hyperbranched polymers have a large
number of terminal maleimide groups, they can cross-link to form a
network when temperature of the battery is elevated, and to form a
protective film on the active material surface for preventing the
diffusion and conductivity of lithium ions, and therefore excellent
shutdown function can be achieved. Examples of such hyperbranched
polymers include hyperbranched polymers obtained by reacting a
maleimide monomer and a dione compound as disclosed in
JP-A-2010-24455 and JP-A-2012-138359.
As maleimide monomers to form a hyperbranched polymer,
monomaleimide monomers, bismaleimide monomers, trismaleimide
monomers and tetra or more-functional multi-maleimide monomers can
be used in combination, but it is preferred that at least a
bismaleimide monomer is contained.
As the bismaleimide monomer, compounds represented by the following
formula (1) or (2) are exemplified.
##STR00001## (in the formula, R.sub.1 is --R--, --R--NH.sub.2--R--,
--C(O)--, --R--C(O)--R--, --R--C(O)--, --O--, --O--O--, --S--,
--S--S--, --S(O)--, --R--S(O)--R--, --SO.sub.2--,
--(C.sub.6H.sub.4)--, --R--(C.sub.6H.sub.4)--R--,
--R--(C.sub.6H.sub.4)--O--, --(C.sub.6H.sub.4)--(C.sub.6H.sub.4)--,
--R--(C.sub.6H.sub.4)--(C.sub.6H.sub.4)--R--, or
--R--(C.sub.6H.sub.4)--(C.sub.6H.sub.4)--O--, R is an alkylene
group having 1 to 8 carbon atoms, --(C.sub.6H.sub.4)-- is a
phenylene group, and --(C.sub.6H.sub.4)--(C.sub.6H.sub.4)--
represents a biphenylene group.)
##STR00002## (in the formula, Y is an alkylene group having 1 to 8
carbon atoms, --C(O)--, --O--, --O--O--, --S--, --S--S--, --S(O)--,
or --SO.sub.2--, and X.sub.1, X.sub.2, X.sub.3, X.sub.4, X.sub.5,
X.sub.6, X.sub.7 and X.sub.8 each independently represent halogen,
hydrogen, alkyl group having 1 to 8 carbon atoms, cycloalkyl group
having 1 to 8 carbon atoms or silylalkyl group having 1 to 8 carbon
atoms.)
Specific examples of the bismaleimide monomer include, but not
particularly limited to, N, N'-bismaleimide-4,4'-diphenylmethane,
1,1'-(methylenelli-4,1-phenylene) bismaleimide, N,
N'-(1,1'-biphenyl-4,4'-diyl)bismaleimide, N,
N'-(4-methyl-1,3-phenylene)bismaleimide,
1,1'-(3,3'-dimethyl-1,1'-biphenyl-4,4'-diyl)bismaleimide, N,
N'-ethylenedimaleimide, N, N'-(1,2-phenylene)dimaleimide, N,
N'-(1,3-phenylene)dimaleimide, N, N'-thiodimaleimide, N,
N'-dithiodimaleimide, N, N'-ketonedimaleimide, N,
N'-methylene-bismaleimide, bismaleimide methyl ether,
1,2-bis-(maleimide)-1,2-ethanethol, N,
N'-4,4'-diphenylether-bismaleimide, or
4,4'-bis(maleimide)diphenylsulfone and the like.
As monomaleimide monomers, trimaleimide monomers and
multi-maleimide monomers, compounds represented by the following
formulae (3) to (6) are exemplified.
##STR00003## (in the formula, R.sub.2 is a phenyl group, an alkyl
group having 1 to 8 carbon atoms or a cycloalkyl group having 5 to
8 carbon atoms)
##STR00004## (in the formula, R.sub.3 each independently represents
a phenylene group, an alkylene group having 1 to 8 carbon atoms or
a cycloalkylene group having 5 to 8 carbon atoms)
##STR00005## (in the formula, R.sub.4 each independently represents
a phenylene group, an alkylene group having 1 to 8 carbon atoms or
a cycloalkylene group having 5 to 8 carbon atoms)
##STR00006## (in the formula, n is 1 to 1000, preferably 1 to 500,
more preferably 5 to 200)
When monomaleimide, trimaleimide and or multi-maleimide monomer is
used in combination with bismaleimide monomer(s), it is preferred
that bismaleimide monomer(s) is contained in the range of 50 to 100
mol %, and more preferably in the range of 50 to 99 mol % based on
the total maleimide monomers.
Examples of the dione compound include, for example, barbituric
acid or its derivatives represented by the following formulae (7)
to (10), and acetylacetone or its derivatives represented by the
following formula (11). In the present specification, the dione
compound does not include a compound having a maleimide group.
##STR00007## (in the formulae, R.sub.1, R.sub.2, R.sub.3, R.sub.4,
R.sub.5, R.sub.6, R.sub.7 and R.sub.8 are each independently, --H,
--CH.sub.3, --C.sub.2H.sub.5, --C.sub.6H.sub.5,
--CH(CH.sub.3).sub.2, --CH.sub.2CH(CH.sub.3).sub.2,
--CH.sub.2CH.sub.2CH(CH.sub.3).sub.2, or
--CH(CH.sub.3)CH.sub.2CH.sub.2CH.sub.3.)
In the case that all of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 in
the formula represent hydrogen, formulae (7) and (8) represents
barbituric acid. Preferably, the dione compound comprises
barbituric acid.
##STR00008## (in the formula, R and R' each are an aliphatic group,
an aromatic group or a heterocyclic group.)
In the formula (11), examples of the aliphatic group include
straight-chain or branched alkyl group having 1 to 6 carbon atoms.
Examples of the aromatic group include phenyl group, naphthyl
group, benzyl group and phenethyl group. Examples of the
heterocyclic group include saturated heterocyclic groups or
unsaturated heterocyclic groups having 4 to 6 membered ring
comprising S, O or N as hetero atom(s).
In the case that all of R and R' each represent a methyl group, the
compound represented by the formula (11) is acetylacetone.
A hyperbranched polymer can be formed by polymerizing a maleimide
monomer containing a bismaleimide monomer and an dione compound in
a solvent containing a Bronsted base.
The molar ratio of the dione compound and the maleimide monomer
(dione Compound:maleimide monomer) is about 1:20 to 4:1. More
preferably, the molar ratio is about 1:5 to 2:1, and more suitably
about 1:3 to 1:1.
Examples of the solvent containing a Bronsted base that can be used
include, for example, N-methylpyrrolidone (NMP), dimethylformamide
(DMF), dimethylacetamide (DMAC), pyrrolidone, N-dodecyl
pyrrolidone, or combinations thereof. In addition, in the
above-mentioned Bronsted base, other solvents that are Bronsted
neutral, such as y-butyrolactone (GBL) may be added. In some cases,
if a solvent containing a Bronsted base is used, the reaction
temperature can be set lower temperature, and therefore it is
preferred.
The reaction temperature is, for example, 20 to 150.degree. C., and
preferably 20 to 100.degree. C.
In the above reaction, by adding the dione batchwise to the
reaction mixture, it is possible to control the degree of
branching, the degree of polymerization, the structure and the like
of the hyperbranched polymer.
The molecular weight of the hyperbranched polymer (mass average
molecular weight) is not particularly limited, but it is preferably
in the range of 400 to 100,000, more preferably in the range of 800
to 20000, and furthermore preferably in the range of 1,000 to
10,000. In the present specification, the mass average molecular
weight is measured by gel permeation chromatography (GPC) using a
calibration curve using monodisperse molecular weight polystyrene
as a standard substance to convert molecular weight.
The degree of branching (%) of the hyperbranched polymer is not
limited in particular, but it is preferably 30 to 100%, more
preferably 40 to 90%, and further preferably 50 to 80%. The degree
of branching of the polymer is represented by:
(D+T)/(D+T+L).times.100(%) wherein T is a number of terminal
portions of the polymer, D is a number of branched portions and L
is a number of unbranched portions.
The hyperbranched polymer preferably has three or more terminal
maleimide groups in one molecule.
As another embodiment of the maleimide resin compound, polyamino
bismaleimides obtained by reacting a bismaleimide with a diamine
are exemplified. The active material may be covered by such a
maleimide resin in a form of prepolymer or resin formed from a
prepolymer and having a mass average molecular weight of, for
example, 400 to about 100,000 (more preferably 800 to 20,000, and
more preferably 100 to 10,000). Polyamino bismaleimide resins can
form a protective film by cross-linking when the temperature of the
battery is elevated. Among these, prepolymers formed from a
bismaleimide compound and an alicyclic diamine have good solvent
solubility, and do not require a long time and high temperature for
curing, as compared with prepolymers formed from a bismaleimide
compound and a straight chain aliphatic diamine or an aromatic
diamine, and therefore they can be preferably used in the present
embodiment.
These polyamino bismaleimide prepolymers can be obtained by mixing
an alicyclic diamine and a bismaleimide compound (alicyclic
diamine:bismaleimide compound=1:1.5 to 3 (molar ratio)) in a
suitable reaction solvent and allowing them to react.
Here, bismaleimide compounds used for the preparation of polyamino
bismaleimide are not particularly limited, and may be a
bismaleimide exemplified in the production of the hyperbranched
polymers described above. Examples of the alicyclic diamine include
4,4'-methylene-biscyclohexane diamine, 1,2-cyclohexanecliamine,
1,3-cyclohexanecliamine, 1,4-cyclohexanecliamine, 1,3-bis
(aminomethyl)cyclohexane, 1,4-bis (aminomethyl)cyclohexane,
isophorone diamine, norbornene diamine,
3(4),8(9)-bis(aminomethyl)tricyclo [5.2.1.02,6]decane diamine and
the like. The bismaleimide compound and the alicyclic diamine each
can be used alone or in combination of two or more.
The reaction solvent when producing polyamino bismaleimide
prepolymer is not particularly limited, but the examples thereof
include 1,4-dioxane, tetrahydrofuran, chloroform, methylene
chloride, methyl ethyl ketone and the like. The reaction conditions
may be set appropriately, for example, at 10 to 60.degree. C. for
10 minutes to 2 hours.
As another embodiment of the maleimide resin compound, compounds
having such a structure that terminal maleimide group(s) is
introduced into any polymeric structures may be exemplified. The
position at which the terminal maleimide group is introduced is not
particularly limited, and it may be a molecular chain terminal of
the polymer structure or it may be an internal non-terminal
position.
As maleimide resins compound, for example, polymers having
maleimide group(s) at molecular chain terminal(s) are preferable.
As the bismaleimide monomer having maleimide group(s) at molecular
chain terminal(s), compounds represented by the following formula
(13) are exemplified. X(OR).sub.n (13) (in formula (13), X
represents a residue obtainable by removing hydroxyl groups from
polyhydric alcohols, n is a number of hydroxyl groups of the
polyhydric alcohol, and R independently represent a moiety of
molecular weight of 100 to 5000 having maleimide group(s) at
molecular chain terminal(s).)
Examples of the polyhydric alcohol to give the residue represented
by X in formula (13) include dihydric or higher alcohols,
cycloalkane polyols and sugar alcohols and sugars and the like.
Examples of polyhydric alcohols include, but not limited to,
dihydric alcohols such as ethylene glycol, propylene glycol,
dipropylene glycol, 1,3- and 1,4-butanecliol, and 1,6-hexanecliol;
trihydric alcohols such as glycerine, trimethylol propane,
trimethylol ethane, and hexane triol; tetravalent alcohols such as
pentaerythritol, methyl glucoside, and diglycerin; polyglycerols
such as triglycerol and tetraglycerol; poly pentaerythritols such
as dipentaerythritol and tripentaerythritol; cycloalkane polyols
such as tetrakis(hydroxymethyl) cyclohexanol; sugar alcohols such
as adonitol, arabitol, xylitol, sorbitol, mannitol, iditol,
talitol, maltitol and dulcitol; sugars such as glucose,
mannoseglucose, mannose, fructose, sorbose, sucrose, lactose,
raffinose and cellulose.
In formula (13), n is an integer of 2 to 20. In applications to
impart shutdown function to a secondary battery to be described
later, it is more preferable that n is 3 or more from the viewpoint
of cross-linking. That is, the polymer is preferably a branched
polymer having maleimide groups at molecular chain terminals
represented by the above formula (13) and having maleimide groups
at respective molecular chain terminals.
In the formula (13), R has a structure in which the maleimide group
is introduced in any of polymer terminals. Here, the polymer
structure is not particularly limited and can be selected suitably
in accordance with the application, but examples thereof include,
for example, acrylic-, polyether-, polycarbonate-, polyurethane-,
epoxy-, alkyd-, and polyester-structure and the like having
molecular weight of 100 to 5000. It is possible to control the
affinity to the electrolyte solution by the density of functional
groups. Since the carbonates and ethers are widely used as
electrolyte solutions of a lithium ion battery, it is preferable
that the polymer structure has any one of the moieties from
polyether-, polycarbonate-, polyurethane-, and polyester-structure
having high affinity with these solutions. Further, the polymer
structure and the maleimide group may be bonded through a linking
group, and the examples of the linking group include, for example,
--O--, --CO--, --CO--O--, --Y--, --O--Y--, --CO--Y-- (wherein, Y is
a linear or branched alkylene group having 1 to 20 carbon atoms)
and the like.
A branched polymer having a polyester structure as R in the above
formula (13) can be obtained by reacting, for example as described
in JP-A 2007-284643, a hydroxyl group-terminated polyester resin
obtained by transesterification of polyester resin using a compound
having 3 or more hydroxyl groups, with maleimide carboxylic
acid.
As examples of branched polymers having a polyester structure as R,
a compound formed from polylactic acid represented by the following
formula (14) is exemplified.
##STR00009## (in the formula (14),
m is an integer from 1 to 10,
R represents, independently, the following formula:
##STR00010## (wherein, p is an integer of 1 to 50, Y is a
straight-chain or branched alkylene group having 1 to 20 carbon
atoms.)
The molecular weight (mass average molecular weight) of the
compound having a structure in which terminal maleimide group is
introduce in the above any polymer structure is not particularly
limited, but it is preferably in the range of 400 to 100,000, more
preferably in the range of 800 to 20,000, and further more
preferably in the range of 1,000 to 10,000.
In the present embodiment, the maleimide compound covers the
surface of an electrode active material (preferably a positive
electrode active material), and the coverage ratio of the maleimide
compound to the surface area of the electrode active material is
preferably at least 5% or more, more preferably 10% or more, more
preferably 30% or more, more preferably 60% or more, further
preferably 70% or more, whereas,it is preferably 98% or less, more
preferably 95% or less, further more preferably 90% or less. In
particular, it is preferably 60% to 95%, and more preferably 70% to
90%. The coverage ratio of the maleimide compound within the above
range is preferred because when the battery becomes excessively
high temperature condition, the movement of lithium ions is
inhibited by cross-linking reaction of the maleimide compound.
Herein, the coverage ratio of the maleimide compound can be
determined by the mapping of nitrogen molecules by SEM-EDS capable
of light element analysis.
In the present embodiment, the maleimide compound covering the
surface of the electrode active material is intended to include
also those present on the surface of the electrode active material
via a first conductive agent, in addition to those in direct
contact with the surface of the electrode active material.
(First Conductive Agent)
A first conductive agent is at least one selected from carbon
nanotubes and carbon nanohorns. These are carbon materials formed
from planar graphene sheets having a 6-membered ring of carbon, and
function as a electric conductive agent in a secondary battery.
Carbon nanotubes have a single layer or a coaxial multilayered
structure in which planar graphene sheets having a 6-membered ring
of carbon are formed into a cylindrical shape, wherein the graphene
plane and the fiber axis may or may not be parallel. Carbon
nanotubes used in the present embodiment are preferably a
multi-layer type, and more preferably a multi-layer type having 2
to 20 layers. Further, both ends of the cylindrical carbon nanotube
may be open, but they are preferably closed with hemispherical
fullerene containing 5-membered rings or 7-membered rings of
carbon. The diameter of the outermost cylinder of carbon nanotubes
is, for example, preferably 500 nm or less, more preferably 200 nm
or less, more preferably 90 nm or less, more preferably 50 nm or
less, and further more preferably 40 nm or less. The lower limit is
not particularly limited, but it is preferably 0.5 nm or more, more
preferably 5 nm or more, further more preferably 10 nm or more.
In carbon nanotubes, it is preferable that the average D/G ratio
obtained from Raman spectroscopy is 0.1 or more, more preferably
0.2 or more, and is preferably 1.2 or less, more preferably 1.1 or
less, more preferably 1.0 or less, more preferably 0.6 or less, and
further preferably 0.4 or less. By using carbon nanotubes having
average D/G ratio obtained by Raman spectroscopic measurement
within the above range, it is possible to improve charge-discharge
cycle characteristics of the battery using the electrode comprising
the same. This is presumably because the carbon nanotubes having
D/G ratio within the above range have few defects, and have low
electronically resistance.
Raman spectrometry is one of the techniques used to evaluate the
crystallinity of the surface of the carbon material. As the Raman
band of graphite, G band (near 1580 to 1600 cm.sup.-1)
corresponding to the in-plane vibration mode and D-band (near 1360
cm.sup.-1) based on defects in the plane are observed. When the
peak intensity of these are taken as IG and ID, lower peak
intensity ratio ID/IG indicates higher degree of graphitization.
ID/IG ratio (referred to as D/G ratio) that is a ratio of the peak
intensity IG of the G band corresponding to in-plane vibration mode
in the circumferential plane of carbon nanotubes and the peak
intensity ID of the D band based on defects in the circumference
plane, is known that can be controlled mainly by heat treatment
temperature, and the higher heat treatment temperature gives small
D/G ratio, and the lower heat treatment temperature gives large D/G
ratio.
As an average D/G ratio by the above Raman spectroscopy, a value
determined by, for example, the following measurement method can be
employed. Arbitrary 50 .mu.m.times.50 .mu.m of the projected image
of the electrode active material is taken as the measurement
surface, and the measurement spot size of Raman spectroscopy is set
.phi.1 .mu.m. Mapping measurement is carried out at a plurality of
locations by shifting by 1 .mu.m by 1 .mu.m in the measurement
surface. From the measured Raman light, D/G ratio is calculated for
individual spots, and the average value thereof is takes as average
D/G ratio. When carbon nanotubes do not exist in some spots and
Raman peak based on carbon nanotubes is not observed, the spots are
excluded from the average calculation.
In addition, carbon nanotubes (preferably carbon nanotubes having
D/G ratio by the Raman spectroscopic measurement of 0.2 or more to
1.2 or less) preferably covers the surface area of the surface of
the electrode active material in the range of 10% or more and 95%
or less, and more preferably 40% or more and 80% or less. In the
present specification, a percentage of the surface of electrode
active material that is covered by carbon nanotubes is described as
"coverage ratio" by carbon nanotubes. When the coverage ratio of
the carbon nanotubes on the electrode active material is 10% or
more and 95% or less, it is possible to improve the cycle
characteristics of the secondary battery using the electrode
comprising an electrode active material covered with a maleimide
resin compound. On the other hand, if the coverage ratio is too
high, the space between the electrode active materials may be
filled with carbon nanotubes, or impregnation of the electrolyte
solution into the space between the electrode active materials may
be insufficient to block the absorption and desorption of lithium
ions, or in the manufacturing process, it may take a long time to
inject an electrolyte solution into the electrode active material
layer.
Method for measuring the area of the covered surface of the
electrode active material by carbon nanotubes having D/G ratio of
0.2 or more and 1.2 or less is performed, as similar to the
measurement of average D/G ratio, by obtaining D/G ratio for
respective spots in an arbitrary measurement surface of the
positive electrode active material layer, and dividing the number
of spots having D/G ratio of 0.2 or more and 1.2 or less by the
total number of measured spots, and expressing the coverage in
percentage to determine coverage ratio.
In this embodiment, the carbon nanotubes covering the surface of
the electrode active material is intended to include also those
present on the surface of the electrode active material via
maleimide compound, in addition to those in direct contact with the
surface of the electrode active material.
Coverage ratio of the electrode active material covered by carbon
nanotubes can be controlled by the type and addition amount of the
carbon nanotubes. When the entire surface of the electrode active
material is covered by the carbon nanotubes, the coverage ratio of
the electrode active material by carbon nanotubes converges to a
value determined by the distribution of D/G ratio of carbon
nanotubes. Therefore, to increase the coverage ratio, the entire
surface of the positive electrode active material layer surface is
preferably covered by using a carbon nanotube material having
narrow distribution width of D/G ratio of 0.2 or more and 1.2 or
less. Thus, the coverage ratio can be controlled by mainly changing
the distribution of D/G ratio of the carbon nanotubes and the
addition amount thereof.
The aspect ratio of the carbon nanotube is not particularly
limited, but it is preferably 100 or more and 1,000 or less. The
aspect ratio of the carbon nanotubes is the ratio of length to
diameter of the carbon nanotube. If the aspect ratio of the carbon
nanotubes is 100 or more, it is easy to cover the electrode active
material by carbon nanotubes, and therefore the conduction between
electrode active materials are attained. If the aspect ratio of the
carbon nanotubes is 1000 or less, it is possible to suppress the
reduction of the workability during a coating process of the
electrode active material, and also it is possible to suppress a
decrease in dispersibility and suppress the increase in viscosity
during production of the slurry. The aspect ratio of carbon
nanotubes is more preferably 150 or more, and further preferably
200 or more, and the upper limit is more preferably 950 or less,
more preferably 900 or less, further preferably 700 or less. It is
particularly preferably 200 or more and 900 or less.
The specific surface area of the carbon nanotube is preferably 40
m.sup.2/g or more and 2000 m.sup.2/g or less. Between the diameter
and the specific surface area of carbon nanotubes, there is
generally a relationship that the specific surface area increases
as the diameter decreases. If the specific surface area is 2000
m.sup.2/g or less, gas generation caused by the reaction of carbon
nanotubes with an electrolyte solution can be suppressed. On the
other hand, if the specific surface area is 40 m.sup.2/g or more,
the surface of a positive electrode active material can be covered
efficiently. Since these carbon nanotubes are in fibrous form, they
can efficiently cover positive electrodeactive material layers, and
also have good characteristics as a electric conductive agent, in
comparison with conventionally used conductive agents in particle
forms such as Ketjen Black having a specific surface area of 800
m.sup.2/g to 1300 m.sup.2/g, or acetylene black having a specific
surface area of 40 m.sup.2/g to 100 m.sup.2/g, or carbon black or
the like.
A carbon nanohorn, if taken as a single piece, has such a shape
that a single graphite sheet is rounded into cylindrical shape
having diameter of about 2 nm to 4 nm wherein the distal end has
conical shape with tip angle of about 20.degree.. A plurality of
these carbon nanohorns gather to form an aggregate, and the
aggregate is classified broadly into Dahlia type and Bud type from
their shapes.
The aggregate having such a shape that a plurality of carbon
nanohorns gather and are connected to each other with conical tips
outside to form a flower-shape of dahlia, is called Dahlia type
carbon nanohorn aggregates.
The aggregate having a bud-like shape is called Bud type carbon
nanohorn aggregate. Whereas plenty of the nanohorns are protruding
from the aggregate surface in Dahlia type carbon nanohorn
aggregate, Bud type carbon nanohorn aggregate has no horn-shaped
protrusion on the surface and has a smooth surface, and thus it has
been described as bud-like shape in contrast to dahlia flower. The
average diameter of Bud type carbon nanohorn aggregate is 80 nm,
and is slightly smaller than the average diameter of Dahlia type
carbon nanohorn aggregate that is 100 nm. The present inventors
speculate that a single nanohorn making up Bud type carbon nanohorn
aggregate is slightly finer and shorter than that making up Dahlia
type. Therefore, the inventors consider that Bud type has smaller
aggregate diameter than Dahlia type (see, Azami et al., the present
inventor, Carbon 45 (2007) 136). The width of a single nanohorn
making up "Bud" type nanohorn aggregate is considered approximately
1.0 nm to 2.0 nm, and length is considered 30 nm to 40 nm, from the
TEM photograph described in the above-mentioned paper.
The carbon nanohorn has, in the state of primary particle, a
diameter of 50 nm to 100 nm. With respect to the size of secondary
particle formed by gathering primary particles, the secondary
particle of the carbon nanohorn is in the range of 0.1 .mu.m to 5
.mu.m. Further, the specific surface area of the carbon nanohorn is
preferably 200 m.sup.2/g or more and 450 m.sup.2/g or less.
In the electrode of the present embodiment, the ratio (M/C) of the
coverage M (%) of the maleimide compound on the electrode active
material to the coverage C (%) of the first conductive agent on the
electrode active material is not particularly limited, but is
preferably 0.6 to 2, and more preferably 0.7 to 1.5. If M/C is
within this range, since the carbon nanotubes suitably cover the
surface of the active material of the positive electrode, the
effect to reduce the electronic resistance between active materials
is obtained, and since the maleimide resin appropriately covers the
surface of the active material within this range, thermal runaway
is reduced. That is, if the ratio (M/C) is in the range of 0.6 to
2, it is more easy to achieve a balance between the effects of
reducing resistance and the effects of preventing thermal runaway
of secondary batteries.
Next, there will be described components of the electrode other
than the above-mentioned maleimide compound and the first
conductive agent.
<Positive Electrode>
For example, the positive electrode preferably has a positive
electrode current collector formed of a metal foil, and a positive
electrode active material applied to one surface or both surfaces
of the positive electrode current collector. The positive electrode
active material is bound on the positive electrode current
collector by a binder for a positive electrode so as to cover it,
to form a positive electrode active material layer. The positive
electrode current collector is arranged to have an extended portion
connected to a positive electrode terminal, and the positive
electrode active material is not applied to this extended
portion.
The positive electrode of the present embodiment preferably
comprises the maleimide compound and the first conductive agent, in
addition to a positive electrode active material and a binder for a
positive electrode.
Examples of an aspect of the positive electrode active material
used in the present embodiment include lithium manganate having a
layered structure or lithium manganate having a spinel structure
such as LiMnO.sub.2, Li.sub.xMn.sub.2O.sub.4 (0<x<2),
Li.sub.2MnO.sub.3, and Li.sub.xMn.sub.1.5Ni.sub.0.5O.sub.4
(0<x<2); LiCoO.sub.2, LiNiO.sub.2 or materials in which a
part of the transition metal in these materials is replaced by
other metal(s); lithium transition metal oxides in which particular
transition metals do not exceed half, such as
LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2; materials in which Li is
excessive as compared with the stoichiometric composition in these
lithium transition metal oxides; materials having olivine structure
such as LiMPO.sub.4, and the like. In addition, materials in which
a part of elements in these metal oxides is substituted by Al, Fe,
P, Ti, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La are
also usable. In particular,
Li.sub..alpha.Ni.sub..beta.Co.sub..gamma.Al.sub..delta.O.sub.2
(1.ltoreq..beta..ltoreq.2, .beta.+.gamma.+.delta.=1,
.beta..gtoreq.0.7, .gamma..ltoreq.0.2) or
Li.sub..alpha.Ni.sub..beta.Co.sub..gamma.Mn.sub.67O.sub.2
(1.ltoreq..alpha..ltoreq.1.2, .beta.+.gamma.+.delta.=1,
.beta..gtoreq.0.6, .gamma..ltoreq.0.2) are preferred. The positive
electrode active materials may be used alone or in combination of
two or more.
Further, it is also possible to use radical material as a positive
electrodeactive material. In addition, as a positive electrode
active material, it is also possible to use an active material that
operates at 4.5 V or higher potential. As a positive electrode
active material that operates at 4.5 V or higher potential,
positive electrode active materials having structure of spinel
type, olivine type, Si complex oxide, layered structure or the like
are exemplified.
Among them, from the viewpoint of high capacity, the positive
electrode active material preferably comprises a lithium nickelate
having a layered structure represented by the following formula:
LiNi.sub.1-xM.sub.xO.sub.2 (wherein, M represents at least one
selected from the group consisting of Mn, Co, and Al, and
0.ltoreq.x.ltoreq.0.8.). x is more preferably
0.ltoreq.x.ltoreq.0.5. Examples of the lithium nickel oxides
represented by the above formula include LiNiO.sub.2,
LiNi.sub.0.33Co.sub.0.33Mn.sub.0.33O.sub.2,
LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2,
LiNi.sub.0.8Mn.sub.0.1Co.sub.0.1O.sub.2,
LiNi.sub.0.5Mn.sub.0.5O.sub.2, LiNi.sub.0.8Mn.sub.0.2O.sub.2 and
the like. The positive electrode active material preferably
comprises these high-capacity active material in an amount of 50
mass % or more, and more preferably 80 mass % or more, and even in
an amount of 100 mass %.
A positive electrode active material according to another aspect of
the present embodiment is not particularly limited as long as it is
a material capable of absorb and desorb lithium, and can be
selected from a number of viewpoints. From the viewpoint of high
energy density, a compound having high capacity is preferably
contained. Examples of the high capacity compound include lithium
acid nickel (LiNiO.sub.2), or lithium nickel composite oxides in
which a part of the Ni of lithium acid nickel is replaced by
another metal element, and layered lithium nickel composite oxides
represented by the following formula (A) are preferred.
Li.sub.yNi.sub.(1-x)M.sub.xO.sub.2 (A) wherein 0.ltoreq.x<1,
0<y 1.2, and M is at least one element selected from the group
consisting of Co, Al, Mn, Fe, Ti, and B.
In addition, from the viewpoint of high capacity, it is preferred
that the content of Ni is high, that is, x is less than 0.5,
further preferably 0.4 or less in the formula (A). Examples of such
compounds include
Li.sub..alpha.Ni.sub..beta.Co.sub..gamma.Mn.sub..delta.O.sub.2
(0<.alpha..ltoreq.1.2, preferably
1.ltoreq..alpha..ltoreq..beta.+.gamma.+.delta.=1, .beta..gtoreq.0.7
and .gamma..ltoreq.0.2) and
Li.sub..alpha.Ni.sub..beta.Co.sub..gamma.Al.sub..delta.O.sub.2
(0>.beta..ltoreq.1.2, preferably 1.ltoreq..alpha..ltoreq.1.2,
.beta.+.gamma.+.delta.=1, .beta..gtoreq.0.7 and .gamma..ltoreq.0.2)
and particularly include
LiNi.sub..beta.Co.sub..gamma.Mn.sub..delta.O.sub.2
(0.75.ltoreq..beta..ltoreq.0.85, 0.05 0.85,
0.05.ltoreq..gamma..ltoreq.0.15, and
0.10.ltoreq..delta..ltoreq.0.20). More specifically, for example,
LiNi.sub.0.8Co.sub.0.05Mn.sub.0.15O.sub.2,
LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2,
LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2, and
LiNi.sub.0.8Co.sub.0.1Al.sub.0.1O.sub.2 may be preferably used.
From the viewpoint of thermal stability, it is also preferred that
the content of Ni does not exceed 0.5, that is, x is 0.5 or more in
the formula (A). In addition, it is also preferred that particular
transition metals do not exceed half. Examples of such compounds
include
Li.sub..alpha.Ni.sub..beta.Co.sub..gamma.Mn.sub..delta.O.sub.2
(0<.alpha..ltoreq.1.2, preferably) 1.ltoreq..alpha..ltoreq.1.2,
.beta.+.gamma.+.delta.=1, 0.2.ltoreq..beta..ltoreq.0.5,
0.1.ltoreq..gamma..ltoreq.0.4, and 0.1.ltoreq..delta..ltoreq.0.4).
More specific examples may include
LiNi.sub.0.4Co.sub.0.3Mn.sub.0.3O.sub.2 (abbreviated as NCM433),
LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2,
LiNi.sub.0.5Co.sub.0.2Mn.sub.0.3O.sub.2 (abbreviated as NCM523),
and LiNi.sub.0.5Co.sub.0.3Mn.sub.0.2O.sub.2 (abbreviated as NCM532)
(also including these compounds in which the content of each
transition metal fluctuates by about 10%).
In addition, two or more compounds represented by the formula (A)
may be mixed and used, and, for example, it is also preferred that
NCM532 or NCM523 and NCM433 are mixed in the range of 9:1 to 1:9
(as a typical example, 2:1) and used. Further, by mixing a material
in which the content of Ni is high (x is 0.4 or less in the formula
(A)) and a material in which the content of Ni does not exceed 0.5
(x is 0.5 or more, for example, NCM433), a battery having high
capacity and high thermal stability can also be formed.
Examples of the positive electrode active materials other than the
above include lithium manganate having a layered structure or a
spinel structure such as LiMnO.sub.2, Li.sub.xMn.sub.2O.sub.4
(0<x<2), Li.sub.2MnO.sub.3, and
Li.sub.xMn.sub.1.5Ni.sub.0.5O.sub.4 (0<x<2); LiCoO.sub.2 or
materials in which a part of the transition metal in this material
is replaced by other metal(s); materials in which Li is excessive
as compared with the stoichiometric composition in these lithium
transition metal oxides; materials having olivine structure such as
LiMPO4, and the like. In addition, materials in which a part of
elements in these metal oxides is substituted by Al, Fe, P, Ti, Si,
Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La are also usable.
The positive electrode active materials described above may be used
alone or in combination of two or more.
Examples of the positive electrode binder include, but not
particularly limited to, for example, polyvinylidene fluoride,
vinylidene fluoride-hexafluoropropylene copolymer, vinylidene
fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer
rubber, polytetrafluoroethylene, polypropylene, polyethylene,
polyimide, polyamideimide, polyacrylic acid and the like. Among
them, polyimide and polyamide-imide are preferable because they
have a strong binding property. The amount of the positive
electrode binder is preferably 2 to 15 parts by mass based on 100
parts by mass of the positive electrode active material, from the
viewpoint of the binding strength and energy density being in a
trade-off relation with each other.
The positive electrode active material layer, in order to reduce
impedance, preferably comprises the above first conductive agent,
and if necessary, a conductive agent (second conductive agent)
other than the first conductive agent may be further contained.
Examples of the second conductive agent include carbonaceous fine
particles such as acetylene black, carbon black and the like, and
carbon black is preferred. The content of the second conductive
agent is preferably 0.5 to 5 wt % based on the weight of the
positive electrode active material.
As the positive electrode current collector, from the view point of
electrochemical stability, aluminum, nickel, stainless steel,
chromium, copper, silver, and alloys thereof are preferred. As the
shape thereof, foil, flat plate, mesh and the like are
exemplified.
<Negative Electrode>
The negative electrode preferably has a negative electrode current
collector formed of metal foil and a negative electrode active
material that is applied on one or both surfaces of the negative
electrode current collector. The negative electrode active material
is bound on the negative electrode current collector by a binder
for a negative electrode so as to cover it, to form a negative
electrode active material layer. The negative electrode current
collector is arranged to have an extended portion connected to a
negative electrode terminal, and the negative electrode active
material is not applied to this extended portion.
Examples of the negative electrode active material include
carbonaceous materials capable of absorbing and desorbing lithium
ions such as cokes, glassy carbons, graphites, non-graphitizable
carbons, and pyrolytic carbons and the like; metals such as Al, Si,
Pb, Sn, Zn, Cd, Sb and the like and alloys of these with lithium;
metal oxides such as LiFe.sub.2O.sub.3, WO.sub.2, MoO.sub.2, SiO,
SiO.sub.2, CuO, SnO, SnO.sub.2, Nb.sub.3O.sub.5,
Li.sub.xTi.sub.2-xO.sub.4 (0.ltoreq.x.ltoreq.1), PbO.sub.2,
PbO.sub.5 and the like; metal sulfides such as SnS, FeS.sub.2 and
the like; metal lithium, lithium alloy; lithium nitrides such as
Li.sub.5(Li.sub.3N), Li.sub.7MnN.sub.4, Li.sub.3FeN.sub.2,
Li.sub.2.5Co.sub.0.5N, Li.sub.3CoN. These materials can be used
alone, or in combination of two or more.
Examples of the negative electrode binder include, but not
particularly limited to, for example, polyvinylidene fluoride,
vinylidene fluoride-hexafluoropropylene copolymer, vinylidene
fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer
rubber, polytetrafluoroethylene, polypropylene, polyethylene,
polyimide, polyamideimide, polyacrylic acid and the like. Among
them, polyimide and polyamide-imide are preferable because they
have a strong binding property. The amount of the negative
electrode binder is preferably 2 to 15 parts by mass based on 100
parts by mass of the negative electrode active material, from the
viewpoint of the binding strength and energy density being in a
trade-off relation with each other.
To the negative electrode active material layer, a conductive agent
may be added in order to reduce impedance. The conductive agent may
comprise the above first conductive agent, and in addition to or in
place of this, a conductive agent (second conductive agent) other
than the first conductive agent may be added. As a second
conductive agent, carbon black, include carbonaceous fine particles
such as acetylene black, carbon black is preferred. The content of
the second conductive agent is preferably 0.1 to 10.0 wt % based on
the weight of the negative electrode active material.
As the negative electrode current collector, from the view point of
electrochemical stability, aluminum, nickel, stainless steel,
chromium, copper, silver, and alloys thereof are preferred. As the
shape thereof, foil, flat plate, mesh and the like are
exemplified.
<Method of Manufacturing Electrode>
Method of manufacturing an electrode comprising a maleimide
compound and the first conductive agent of the present embodiment
is not particularly limited. Typically, the method comprises a step
of mixing and stirring a maleimide compound, a first conductive
agent, an electrode active material, an electrode binder, and if
needed, a second conductive agent other than the first conductive
agent in a solvent whereby preparing a electrode slurry, and a step
of coating the electrode slurry on a collector and drying it. In
the step of preparing the electrode slurry, the order of mixing the
materials is not particularly limited. For example, a maleimide
compound, a first conductive agent, an electrode active material
and a binder may be mixed at the same time in a solvent; or a
maleimide compound and a first conductive agent may be mixed in a
solvent to prepare a dispersion of the first conductive agent, and
then it is mixed with an electrode active material and a binder; or
a maleimide compound and an electrode active material may be mixed
in a solvent, and further mixing and stirring may be performed
after a first conductive agent and a binder are added to the
mixture. Temperature for drying the electrode slurry on the current
collector is preferably less than 180.degree. C. The solvent that
can be used is not particularly limited as long as it dissolves the
maleimide resin compound and does not dissolve the active material,
and the examples thereof include, N-methylpyrrolidone (NMP),
dimethylformamide (DMF), climethylacetamide (DMAC), pyrrolidone and
N-dodecyl pyrrolidone. The step of preparing the electrode slurry
by stirring and mixing may be usually carried out at room
temperature, for 15 minutes or longer, preferably for 30 minutes or
longer, and preferably within 3 days in view of the manufacturing
process. the electrode active material covered with a maleimide
compound and/or a first conductive agent may be, if necessary,
purified by filtration, washing, drying and the like.
On preparing the electrode slurry, the amount of the maleimide
compound is preferably 0.05 to 10 wt %, more preferably 0.1 to 10
wt %, and further preferably 0.5 to 3 wt % based on the weight of
electrode active material. The amount of the first conductive agent
is preferably 0.2 to 5.0 wt %, more preferably 0.5 to 5.0 wt %,
further preferably 1.0 to 3.0 wt % based on the weight of electrode
active material.
The amounts of the maleimide compound and the first conductive
agent to be blended in the electrode slurry are, although it
depends on the kind of the maleimide compound and the first
conductive agent, preferably in a weight ratio of 1:10 to 10:1 for
example.
<Basic Structure of Secondary Battery>
There are various types of secondary batteries depending on a
structure of electrode or a shape, such as cylindrical type, flat
spirally wound prismatic type, laminated square shape type, coin
type, flat wound laminated type and layered laminate type or the
like. The present invention is applicable to any of these
types.
FIG. 1 shows a cross-sectional view of a laminate type lithium ion
secondary battery according to the present embodiment. As shown in
FIG. 1, a lithium ion secondary battery according to the present
embodiment have a positive electrode comprising a positive
electrode current collector 3 made of a metal such as aluminum foil
and a positive electrode active material layer 1 containing a
positive electrode active material provided thereon, and a negative
electrode comprising an anode current collector 4 made of metal
such as copper foil and a negative electrode active material layer
2 containing a negative electrode active material provided thereon.
The positive electrode and the negative electrode are stacked via a
separator 5 made of a nonwoven fabric or polypropylene microporous
membrane so that the positive electrode active material layer 1 and
the anode active material layer 2 are opposed to each other. This
electrode pair is housed in an aluminum laminate film or the like
inside the container formed by an outer packaging laminate 6. A
positive electrode lead terminal 8 is connected to the positive
electrode current collector 3, a negative electrode lead terminal 7
is connected to the negative electrode current collector 4, and
these tabs are drawn out of the container. An electrolyte solution
is injected into the container, and the container is sealed. It is
also preferred that an electrode element (also referred to as
"battery element" or "electrode stack") may have, as shown in FIG.
2, an arrangement in which a plurality of positive electrodes and a
plurality of negative electrodes are stacked via separators.
As another embodiment, a secondary battery having a structure as
shown in FIG. 3 and FIG. 4 may be provided. This secondary battery
comprises a battery element 20, a film package 10 housing the
battery element 20 together with an electrolyte, and a positive
electrode tab 51 and a negative electrode tab 52 (hereinafter these
are also simply referred to as "electrode tabs").
In the battery element 20, a plurality of positive electrodes 30
and a plurality of negative electrodes 40 are alternately stacked
with separators 25 sandwiched therebetween as shown in FIG. 4. In
the positive electrode 30, an electrode material 32 is applied to
both surfaces of a metal foil 31, and also in the negative
electrode 40, an electrode material 42 is applied to both surfaces
of a metal foil 41 in the same manner. The present invention is not
necessarily limited to stacking type batteries and may also be
applied to batteries such as a winding type.
In the secondary battery in FIGS. 1 and 2, the electrode tabs are
drawn out on both sides of the package, but a secondary battery to
which the present invention may be applied may have an arrangement
in which the electrode tabs are drawn out on one side of the
package as shown in FIG. 3. Although detailed illustration is
omitted, the metal foils of the positive electrodes and the
negative electrodes each have an extended portion in part of the
outer periphery. The extended portions of the negative electrode
metal foils are brought together into one and connected to the
negative electrode tab 52, and the extended portions of the
positive electrode metal foils are brought together into one and
connected to the positive electrode tab 51 (see FIG. 4). The
portion in which the extended portions are brought together into
one in the stacking direction in this manner is also referred to as
a "current collecting portion" or the like.
The film package 10 is composed of two films 10-1 and 10-2 in this
example. The films 10-1 and 10-2 are heat-sealed to each other in
the peripheral portion of the battery element 20 and hermetically
sealed. In FIG. 3, the positive electrode tab 51 and the negative
electrode tab 52 are drawn out in the same direction from one short
side of the film package 10 hermetically sealed in this manner.
Of course, the electrode tabs may be drawn out from different two
sides respectively. In addition, regarding the arrangement of the
films, in FIG. 3 and FIG. 4, an example in which a cup portion is
formed in one film 10-1 and a cup portion is not formed in the
other film 10-2 is shown, but other than this, an arrangement in
which cup portions are formed in both films (not illustrated), an
arrangement in which a cup portion is not formed in either film
(not illustrated), and the like may also be adopted.
<Electrolyte Solution>
As an electrolyte solution used in the present embodiment,
non-aqueous electrolyte solutions containing a lithium salt
(supporting salt), and a non-aqueous solvent for dissolving the
support salt are used.
As the non-aqueous solvents, aprotic organic solvents such as
carbonic acid esters (open chain or cyclic carbonates), carboxylic
acid esters (open chain or cyclic carboxylic acid esters),
phosphoric acid esters and the like may be used.
Examples of the carbonic acid ester solvents include, cyclic
carbonates such as propylene carbonate (PC), ethylene carbonate
(EC), butylene carbonate (BC) and vinylene carbonate (VC); open
chain carbonates such as dimethyl carbonate (DMC), diethyl
carbonate (DEC), ethyl methyl carbonate (EMC) and dipropyl
carbonate (DPC); and propylene carbonate derivatives.
Examples of the carboxylic acid ester solvents include aliphatic
carboxylic acid esters such as methyl formate, methyl acetate and
ethyl propionate; and lactones such as y-butyrolactone.
Among these, carbonic acid esters (cyclic or linear carbonate),
such as ethylene carbonate (EC), propylene carbonate (PC), butylene
carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC),
diethyl carbonate (DEC), ethyl methyl carbonate (MEC), and dipropyl
carbonate (DPC), are preferred.
Examples of the phosphoric acid esters include, for example,
trimethyl phosphate, triethyl phosphate, tripropyl phosphate,
trioctyl phosphate, triphenyl phosphate, and the like.
Examples of solvents that can be contained in the nonaqueous
electrolyte solution include, in addition to those mentioned above,
for example, ethylene sulfite (ES), propane sultone (PS), butane
sultone (BS), clioxathiolane-2,2-dioxide (DD), sulfolene,
3-methylsulfolene, sulfolane (SL), succinic anhydride (SUCAH),
propionic anhydride, acetic anhydride, maleic anhydride, diallyl
carbonate (DAC), dimethyl 2,5-clioxahexaneclionate, dimethyl
2,5-dioxahexaneclionate, furan, 2,5-dimethylfuran, diphenyl sulfide
(DPS), climethoxyethane (DME), dimethoxymethane (DMM), cliethoxy
ethane (DEE), ethoxymethoxyethane, chloroethylene carbonate,
dimethyl ether, methyl ethyl ether, methyl propyl ether, ethyl
propyl ether, dipropyl ether, methyl butyl ether, diethyl ether,
phenyl methyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran
(2-MeTHF), tetrahydropyran (THP), 1,4-dioxane (DIOX),
1,3-clioxolane (DOL), methyl acetate, ethyl acetate, propyl
acetate, isopropyl acetate, butyl acetate, methyl clifluoromethyl
acetate, methyl propionate, ethyl propionate, propyl propionate,
methyl formate, ethyl formate, ethyl butyrate, isopropyl butyrate,
methyl isobutyrate, methyl cyanoacetate, vinyl acetate, diphenyl
disulfide, dimethyl sulfide, diethyl sulfide, adiponitrile,
valeronitrile, glutaronitrile, malononitrile, succinonitrile,
pimelonitrile, suberonitrile, isobutyronitrile, biphenyl,
thiophene, methyl ethyl ketone, fluorobenzene, hexafluorobenzene,
carbonates electrolyte, glyme, ether, acetonitrile, propionitrile,
y-butyrolactone, y-valerolactone, dimethyl sulfoxide (DMSO), ionic
liquids, phosphazene, aliphatic carboxylic acid esters such as
methyl formate, methyl acetate, and ethyl propionate, or compounds
in which a part of hydrogen atoms of these compounds is/are
substituted with fluorine atom(s).
Non-aqueous solvent may be used alone, or in combination of two or
more.
As the supporting salt in the present embodiment, lithium salts
that can be used in usual lithium ion batteries such as LiPF.sub.6,
LiAsF.sub.6, LiAlCl.sub.4, LiClO.sub.4, LiBF.sub.4, LiSbF.sub.6,
LiCF.sub.3SO.sub.3, LiC.sub.4F.sub.9SO.sub.3,
LiC(CF.sub.3SO.sub.2).sub.3, LiN(CF.sub.3SO.sub.2).sub.2 and the
like can be used. Supporting salts may be used alone or in
combination of two or more.
The separators that can be used include, but not particularly
limited, porous films or nonwoven fabrics formed of, for example,
polypropylene, polyethylene, fluororesin, polyamide, polyimide,
polyester, polyphenylene sulfide and the like; or those in which
inorganic materials such as silica, alumina, or glass are adhered
or bonded to these base materials, or inorganic materials alone are
processed into nonwoven fabrics or cloths. As a separator, those
obtained by laminating these material may be also used.
An outer package can be appropriately selected as long as it has
stability in an electrolyte solution and sufficient steam barrier
properties. For example, in the case of a laminate type secondary
battery, laminate films, such as polypropylene, polyethylene or the
like coated with aluminium or silica can be used as the outer
package. The outer package may be constituted by a single member or
may be constituted by combining a plurality of members.
<Method of Manufacturing Secondary Battery>
The secondary battery according to the present embodiment can be
manufactured according to conventional methods. For example, it is
possible to manufacture a lithium ion secondary battery of the
stacked laminate type in the following manner. First, according to
the above, a positive electrode having a positive electrode active
material layer provided on a positive electrode current collector,
and a negative electrode having a negative electrode active
material layer provided on a negative electrode current collector
are formed.
Then, in dry air or inert atmosphere, the positive electrode and
the negative electrode are placed to oppose to each other via a
separator to form an electrode pair and to form an electrode stack
having necessary numbers of laminations in accordance with a
desired capacity. The electrode stack has a positive terminal to be
connected to the positive electrode current collector, and a
negative electrode terminal to be connected to the negative
electrode current collector. Then, the electrode stack is
accommodated in the outer package (container), by injecting a
non-aqueous electrolyte solution and impregnating the electrode
with the electrolyte solution. Then, the opening of the package is
sealed to complete a secondary battery.
<Assembled Battery>
A plurality of secondary batteries according to the present
embodiment may be combined to form an assembled battery. The
assembled battery may be configured by connecting at least two
secondary batteries according to the present embodiment in series
or in parallel or in combination of both. The connection in series
and/or parallel makes it possible to adjust the capacitance and
voltage freely. The number of secondary batteries included in the
assembled battery can be set appropriately according to the battery
capacity and output.
<Vehicle>
The secondary battery or the assembled battery according to the
present embodiment can be used in vehicles. Vehicles according to
an embodiment of the present invention include hybrid vehicles,
fuel cell vehicles, electric vehicles (besides four-wheel vehicles
(cars, trucks, commercial vehicles such as buses, light
automobiles, etc.) two-wheeled vehicle (bike) and tricycle), and
the like. Since these vehicles are equipped with a secondary
battery according to the present embodiment, a high reliability and
long life are ensured. The vehicles according to the present
embodiment is not limited to automobiles, it may be a variety of
power source of other vehicles, such as a moving body like a
train.
<Power Storage Equipment>
The secondary battery or the assembled battery according to the
present embodiment can be used in power storage equipment. The
power storage devices according to the present embodiment include,
for example, those which is connected between the commercial power
supply and loads of household appliances and used as a backup power
source or an auxiliary power in the event of power outage or the
like, or those used as a large scale power storage that stabilize
power output with large time variation supplied by renewable
energy, for example, solar power generation.
A preferable aspect of the present embodiment includes a secondary
battery electrode comprising a thermal activation material and a
conductive agent, wherein the conductive agent comprises at least
one selected from carbon nanotubes and carbon nanohorns. In the
secondary battery comprising the secondary battery electrode, when
it becomes excessively high temperature state in the overcharge or
the like, the diffusion and conduction of lithium ions are
suppressed by cross-linking reaction or the like of the thermal
activation material, and the thermal runaway of the secondary
battery is suppressed.
EXAMPLE
Hereafter, an embodiment of the present invention will be explained
in details by using examples, but the present invention is not
limited to these examples.
Materials used in Examples and Comparative Examples are shown
below.
<Positive Electrode Active Material>
Positive electrode active material A:
LiNi.sub.0.8Co.sub.0.2O.sub.2
Positive electrode active material B:
LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2
Positive electrode active material C:
LiNi.sub.0.8Mn.sub.0.1Co.sub.0.1O.sub.2
<Conductive agent>
In the following examples and comparative examples, carbon
nanotubes A, B and C are described as "CNT-A", "CNT-B" and "CNT-C",
respectively, and carbon black is described as "CB".
Average D/G ratio by Raman spectroscopy, average diameter, and
aspect ratio of carbon nanotubes A to C and carbon black used in
Examples and Comparative Examples are shown in Table 1. Raman
spectrometry is one of the techniques often used to evaluate the
crystallinity of the surface of the carbon material. As the Raman
band of graphite, G band (near 1580 to 1600 cm.sup.-1)
corresponding to the in-plane vibration mode and D-band (near 1360
cm.sup.-1) based on defects in the plane are observed. When the
peak intensity of these are taken as IG and ID, lower peak
intensity ratio ID/IG indicates higher degree of graphitization.
ID/IG ratio (referred to as D/G ratio) that is a ratio of the peak
intensity IG of the G band corresponding to in-plane vibration mode
in the circumferential plane of carbon nanotubes and the peak
intensity ID of the D band based on defects in the circumference
plane, is known that can be controlled mainly by heat treatment
temperature, and the higher heat treatment temperature gives small
D/G ratio, and the lower heat treatment temperature gives large D/G
ratio.
TABLE-US-00001 TABLE 1 average diameter conductive agent D/G ratio
(nm) aspect ratio carbon nanotube A 0.31 20 900 (CNT-A) carbon
nanotube B 0.81 20 500 (CNT-B) carbon nanotube C 1.10 20 200
(CNT-C) carbon black 1.10 60 1.0 (CB)
<Maleimide Compound>
Synthesis of maleimide resin compound (hereinafter, "the maleimide
compound A")
(1) To 250 mL three-neck round-bottom flask, 4.5 g of
4,4'-bismaleimide cliphenylmethane was added and 60 g of NMP
solvent was added. The mixture was heated to 70.degree. C. and
stirred thoroughly to dissolve 4,4'-bismaleimide diphenylmethane
completely in NMP solvent (R1).
(2) 1.8 g of barbituric acid (BTA) powder was added to 40 g of NMP
solvent, and was stirred thoroughly to uniformly disperse BTA in
NMP solvent as an emulsion (R2).
(3) (R2) wad divided into 8 equal parts, and one part was added
batchwise every 15 minutes into (R1), and the mixture was stirred
thoroughly to allow the thermal polymerization reaction of the
double bond of 4,4'-bismaleimide cliphenylmethane to proceed.
(4) After all 8 parts of (R2) were added to (R1), the reaction was
allowed to proceed for additional 4 hours. This gave a maleimide
resin solution (R3) containing the maleimide compound A.
Example 1
Polyvinylidene fluoride (PVdF) as a binder in an amount of 3 mass %
based on the mass of the positive electrode active material,
maleimide compound A in an amount of 0.1 mass % based on the mass
of the positive electrode active material, carbon nanotube A as a
first conductive agent in an amount of 2.0 mass % based on the mass
of the positive electrode active material, and layered lithium
nickel oxides (LiNi.sub.0.8Co.sub.0.2O.sub.2) having an average
particle diameter of 8 .mu.m in a remaining amount other than the
above, are dispersed uniformly in NMP using a rotation revolution
type three-axis mixer excellent in stirring and mixing, to prepare
a positive electrode slurry. The positive electrode slurry were
uniformly applied to a positive electrode current collector of
aluminum foil with a thickness of 20 .mu.m using a coater. After
drying by evaporating NMP, the back side was also coated in the
same way. After drying, the density was adjusted by roll press, to
prepare positive electrode active material layers on both sides of
the current collector. Mass per unit area of the positive electrode
active material layer was 50 mg/cm.sup.2.
96 mass % of massive artificial graphite having an amorphous
carbon-based surface coating of average particle diameter of 10
.mu.m as a negative electrode active material, 2 mass % of SBR as a
binder, 1 mass % of CMC as a thickener, and 1 mass % of carbon
black were added to and dispersed in water, to prepare a negative
electrode slurry. The negative electrode slurry were uniformly
applied to a negative electrode current collector of copper foil
with a thickness of 10 .mu.m using a coater. After drying by
evaporating water, the density was adjusted by roll press, to
prepare negative electrode active material layers. Mass per unit
area of the negative electrode active material layer was 30
mg/cm.sup.2.
As an electrolyte solution, 1 mol/L of LiPF.sub.6 as an electrolyte
was dissolved in a solvent of ethylene carbonate (EC):diethyl
carbonate (DEC)=30:70 (vol %).
The resulting positive electrode was cut into 13 cm.times.7 cm, and
the negative electrode was to cut into 12 cm.times.6 cm. The both
surfaces of the positive electrode was covered by a polypropylene
separator of 14 cm.times.8 cm, the negative active material layer
was disposed thereon so as to face the positive electrode active
material layer, to prepare an electrode stack. Next, the electrode
stack was sandwiched by two sheets of aluminum laminate film of 15
cm.times.9 cm, the three sides excluding one long side were heat
sealed with a seal width of 8 mm. After injecting the electrolyte
solution, the remaining side was heat sealed, to produce a laminate
cell type battery.
<Coverage of Conductive Agent on Surface of Positive Electrode
Active Material>
D/G ratio by Raman spectroscopy was adopted for the measurement of
coverage of the conductive agent on the surface of the positive
electrode active material (carbon nanotube (CNT) and/or carbon
black). Arbitrary 50 .mu.m.times.50 .mu.m of the projected image of
the positive electrode active material is taken as a the
measurement surface, and the measurement spot size of Raman
spectroscopy is set .phi.1 .mu.m. Mapping measurement (676 spots)
is carried out by shifting by 1 .mu.m by 1 .mu.m in the measurement
surface. From the measured Raman light, D/G ratio is calculated for
individual spots. The coverage ratio of the conductive agent was
determined by dividing the number of spots having D/G ratio in the
range of 0.2 to 1.1 determined by Raman spectroscopy described
above by the number of all measured spots, and expressing the
numerical value as percentage.
The coverage ratio of the conductive agent on the surface of the
positive electrode active material will be described as C (%) in
Tables 2 to 5.
<Coverage of Maleimide Compound on Surface of Positive Electrode
Active Material>
For the method of measuring coverage ratio of maleimide compound of
on the surface of the active material, energy dispersive X-ray
spectrometry was used. As energy dispersive X-ray analysis, values
determined by the following measurement method can be employed.
Arbitrary 50 .mu.m.times.50 .mu.m of the projected image of the
electrode active material is taken as a the measurement surface,
and the measurement spot size of energy dispersive X-ray analysis
is set .phi.1 .mu.m. Mapping measurement (676 points) is carried
out by shifting by 1 .mu.m by 1 .mu.m in the measurement surface.
By measuring nitrogen (N)-originated peak, the coverage ratio of
the maleimide compound is determined. At portions where carbon
nanotubes cover the positive electrode, since carbon C is measured,
the spot is excluded from the calculation of the average of the
maleimide compound.
The coverage ratio of the maleimide compound on the surface of the
positive electrode active material will be described as M (%) in
Tables 2 to 5.
(Cycle Characteristics)
<Measurement of Capacity Retention Ratio>
1000 times of charge-discharge cycle test were performed in a
thermostatic oven at 45.degree. C. to measure the capacity
retention ratio and to evaluate the lifetime. In the charge, the
secondary battery was charged at 1 C up to maximum voltage of 4.2 V
and then subjected to constant voltage charge at 4.2 V, and the
total charge time was 2.5 hours. In the discharge, the secondary
battery was subjected to constant current discharge at 1 C to 2.5
V. Although the charge and discharge cycles were performed at
relatively high temperature of 45.degree. C., this is because it is
possible to identify cell characteristics deterioration at an early
stage. The capacity after the charge-discharge cycle test was
measured, and the ratio to the capacity before the charge-discharge
cycle test was calculated. The results are shown in Tables 2 to
5.
(Safety Test)
<Overcharge Test>
Batteries of Examples 1 to 38 and Comparative Examples 1 to 46 were
subjected to the overcharge test described in JIS C8712. The stack
portion of batteries are fixed with flat press plates in constant
gap in accordance with the thickness of the battery. Overcharge
test was carried out at 10 A. The surface temperature of the
battery reached 95.degree. C. at the voltage of about 6 V, and
after having reached to 10V, a battery that has finished test
without emitting smoke is rated as .smallcircle., and a battery
that has emitted smoke was rated as .times..
Evaluation criteria are as follows. .smallcircle.: after having
reached to 10V, the test finished without emitting gas. x: emitted
smoke.
The coverage ratios of the maleimide compound and conductive agent
on the surface of the positive electrode active material, the
measurement results of cycle characteristics, and the evaluation
results of safety test are shown in Tables 2 to 5.
Example 2 to 38
Lithium ion secondary batteries were produced in the same manner as
in Example 1, except that the kind and the blending amount of
positive electrode active material, maleimide compound and
conductive agent were changed as shown in Tables 2 and 3. The
measurement of cycle characteristics and safety test (overcharge
test) were carried out.
Comparative Examples 1 to 46
Lithium ion secondary batteries were produced in the same manner as
in Example 1, except that either one of maleimide compound and
carbon nanotube is not used and the kind and the blending amount of
each material were changed as shown in Tables 4 and 5. The
measurement of cycle characteristics and safety test (overcharge
test) were carried out.
TABLE-US-00002 TABLE 2 cycle first second conductive character-
positive maleimide conductive conductive maleimide agent istics
electrode compound agent agent coverage coverage 45.degree. C.
active Weight Weight Weight ratio ratio M/C @1000 cy material (wt
%) (wt %) (wt %) M (%) C (%) ratio (%) safety Ex. 1 A A 0.1 CNT-A
2.0 none 0.0 10 65 0.15 90 .smallcircle. Ex. 2 A A 0.25 CNT-A 2.0
none 0.0 30 70 0.43 88 .smallcircle. Ex. 3 A A 0.5 CNT-A 2.0 none
0.0 50 75 0.67 86 .smallcircle. Ex. 4 A A 1.0 CNT-A 2.0 none 0.0 80
80 1.00 85 .smallcircle. Ex. 5 A A 2.5 CNT-A 2.0 none 0.0 95 85
1.12 83 .smallcircle. Ex. 6 A A 0.1 CNT-B 2.0 none 0.0 10 67 0.15
91 .smallcircle. Ex. 7 A A 0.25 CNT-B 2.0 none 0.0 30 72 0.42 89
.smallcircle. Ex. 8 A A 0.5 CNT-B 2.0 none 0.0 50 77 0.65 87
.smallcircle. Ex. 9 A A 1.0 CNT-B 2.0 none 0.0 70 82 0.85 86
.smallcircle. Ex. 10 A A 2.5 CNT-B 2.0 none 0.0 95 87 1.09 84
.smallcircle. Ex. 11 A A 1.0 CNT-B 0.5 none 0.0 80 65 1.23 80
.smallcircle. Ex. 12 A A 1.0 CNT-B 1.0 none 0.0 80 70 1.14 81
.smallcircle. Ex. 13 A A 1.0 CNT-B 1.5 none 0.0 80 75 1.07 83
.smallcircle. Ex. 14 A A 1.0 CNT-B 2.5 none 0.0 80 90 0.89 87
.smallcircle. Ex. 15 A A 1.0 CNT-B 0.5 CB 2.0 80 68 1.18 81
.smallcircle. Ex. 16 A A 1.0 CNT-B 1.0 CB 2.0 80 73 1.10 82
.smallcircle. Ex. 17 A A 1.0 CNT-B 1.5 CB 2.0 80 78 1.03 84
.smallcircle. Ex. 18 A A 1.0 CNT-B 2.5 CB 2.0 80 93 0.86 88
.smallcircle. Ex. = Example
TABLE-US-00003 TABLE 3 cycle first second conductive character-
positive maleimide conductive conductive maleimide agent istics
electrode compound agent agent coverage coverage 45.degree. C.
active Weight Weight Weight ratio ratio M/C @1000 cy material (wt
%) (wt %) (wt %) M (%) C (%) ratio (%) safety Ex. 19 B A 1.0 CNT-C
0.5 none 0.0 80 65 1.23 82 .smallcircle. Ex. 20 B A 1.0 CNT-C 1.0
none 0.0 80 70 1.14 83 .smallcircle. Ex. 21 B A 1.0 CNT-C 1.5 none
0.0 80 75 1.07 85 .smallcircle. Ex. 22 B A 1.0 CNT-C 2.0 none 0.0
80 80 1.00 87 .smallcircle. Ex. 23 B A 1.0 CNT-C 2.5 none 0.0 80 90
0.89 89 .smallcircle. Ex. 24 B A 1.0 CNT-C 0.5 CB 2.0 80 68 1.18 83
.smallcircle. Ex. 25 B A 1.0 CNT-C 1.0 CB 2.0 80 73 1.10 84
.smallcircle. Ex. 26 B A 1.0 CNT-C 1.5 CB 2.0 80 78 1.03 86
.smallcircle. Ex. 27 B A 1.0 CNT-C 2.0 CB 2.0 80 83 0.96 88
.smallcircle. Ex. 28 B A 1.0 CNT-C 2.5 CB 2.0 80 93 0.86 90
.smallcircle. Ex. 29 C A 1.0 CNT-C 0.5 none 0.0 80 65 1.23 81
.smallcircle. Ex. 30 C A 1.0 CNT-C 1.0 none 0.0 80 70 1.14 82
.smallcircle. Ex. 31 C A 1.0 CNT-C 1.5 none 0.0 80 75 1.07 84
.smallcircle. Ex. 32 C A 1.0 CNT-C 2.0 none 0.0 80 80 1.00 86
.smallcircle. Ex. 33 C A 1.0 CNT-C 2.5 none 0.0 80 90 0.89 88
.smallcircle. Ex. 34 C A 1.0 CNT-C 0.5 CB 2.0 80 68 1.18 82
.smallcircle. Ex. 35 C A 1.0 CNT-C 1.0 CB 2.0 80 73 1.10 83
.smallcircle. Ex. 36 C A 1.0 CNT-C 1.5 CB 2.0 80 78 1.03 85
.smallcircle. Ex. 37 C A 1.0 CNT-C 2.0 CB 2.0 80 83 0.96 87
.smallcircle. Ex. 38 C A 1.0 CNT-C 2.5 CB 2.0 80 93 0.86 89
.smallcircle.
TABLE-US-00004 TABLE 4 cycle first second conductive character-
positive maleimide conductive conductive maleimide agent istics
electrode compound agent agent coverage coverage 45.degree. C.
active Weight Weight Weight ratio ratio M/C @1000 cy material (wt
%) (wt %) (wt %) M (%) C (%) ratio (%) safety Comp-Ex. 1 A none 0.0
CNT-B 2.0 none 0.0 0 65 0.00 88 x Comp-Ex. 2 A none 0.0 CNT-B 2.0
none 0.0 0 70 0.00 86 x Comp-Ex. 3 A none 0.0 CNT-B 2.0 none 0.0 0
75 0.00 84 x Comp-Ex. 4 A none 0.0 CNT-B 2.0 none 0.0 0 80 0.00 83
x Comp-Ex. 5 A none 0.0 CNT-B 2.0 none 0.0 0 85 0.00 81 x Comp-Ex.
6 A none 0.0 CNT-C 2.0 none 0.0 0 67 0.00 89 x Comp-Ex. 7 A none
0.0 CNT-C 2.0 none 0.0 0 72 0.00 87 x Comp-Ex. 8 A none 0.0 CNT-C
2.0 none 0.0 0 77 0.00 85 x Comp-Ex. 9 A none 0.0 CNT-C 2.0 none
0.0 0 82 0.00 84 x Comp-Ex. 10 A none 0.0 CNT-C 2.0 none 0.0 0 87
0.00 82 x Comp-Ex. 11 A none 0.0 CNT-B 0.5 none 0.0 0 65 0.00 78 x
Comp-Ex. 12 A none 0.0 CNT-B 1.0 none 0.0 0 70 0.00 79 x Comp-Ex.
13 A none 0.0 CNT-B 1.5 none 0.0 0 75 0.00 81 x Comp-Ex. 14 A none
0.0 CNT-B 2.0 none 0.0 0 80 0.00 83 x Comp-Ex. 15 A none 0.0 CNT-B
2.5 none 0.0 0 90 0.00 85 x Comp-Ex. 16 A none 0.0 CNT-B 0.5 CB 2.0
0 68 0.00 79 x Comp-Ex. 17 A none 0.0 CNT-B 1.0 CB 2.0 0 73 0.00 80
x Comp-Ex. 18 A none 0.0 CNT-B 1.5 CB 2.0 0 78 0.00 82 x Comp-Ex.
19 A none 0.0 CNT-B 2.0 CB 2.0 0 83 0.00 84 x Comp-Ex. 20 A none
0.0 CNT-B 2.5 CB 2.0 0 93 0.00 86 x Comp-Ex. = Comparative
Example
TABLE-US-00005 TABLE 5 cycle first second conductive character-
positive maleimide conductive conductive maleimide agent istics
electrode compound agent agent coverage coverage 45.degree. C.
active Weight Weight Weight ratio ratio M/C @1000 cy material (wt
%) (wt %) (wt %) M (%) C (%) ratio (%) safety Comp-Ex. 21 B none
0.0 CNT-B 0.5 none 0.0 0 65 0.00 80 x Comp-Ex. 22 B none 0.0 CNT-B
1.0 none 0.0 0 70 0.00 81 x Comp-Ex. 23 B none 0.0 CNT-B 1.5 none
0.0 0 75 0.00 83 x Comp-Ex. 24 B none 0.0 CNT-B 2.0 none 0.0 0 80
0.00 85 x Comp-Ex. 25 B none 0.0 CNT-B 2.5 none 0.0 0 90 0.00 87 x
Comp-Ex. 26 B none 0.0 CNT-B 0.5 CB 2.0 0 68 0.00 81 x Comp-Ex. 27
B none 0.0 CNT-B 1.0 CB 2.0 0 73 0.00 82 x Comp-Ex. 28 B none 0.0
CNT-B 1.5 CB 2.0 0 78 0.00 84 x Comp-Ex. 29 B none 0.0 CNT-B 2.0 CB
2.0 0 83 0.00 86 x Comp-Ex. 30 B none 0.0 CNT-B 2.5 CB 2.0 0 93
0.00 88 x Comp-Ex. 31 C none 0.0 CNT-B 0.5 none 0.0 0.0 65 0.00 79
x Comp-Ex. 32 C none 0.0 CNT-B 1.0 none 0.0 0.0 70 0.00 80 x
Comp-Ex. 33 C none 0.0 CNT-B 1.5 none 0.0 0.0 75 0.00 82 x Comp-Ex.
34 C none 0.0 CNT-B 2.0 none 0.0 0.0 80 0.00 84 x Comp-Ex. 35 C
none 0.0 CNT-B 2.5 none 0.0 0.0 90 0.00 86 x Comp-Ex. 36 C none 0.0
CNT-B 0.5 CB 2.0 0.0 68 0.00 80 x Comp-Ex. 37 C none 0.0 CNT-B 1.0
CB 2.0 0.0 73 0.00 81 x Comp-Ex. 38 C none 0.0 CNT-B 1.5 CB 2.0 0.0
78 0.00 83 x Comp-Ex. 39 C none 0.0 CNT-B 2.0 CB 2.0 0.0 83 0.00 85
x Comp-Ex. 40 C none 0.0 CNT-B 2.5 CB 2.0 0.0 93 0.00 87 x Comp-Ex.
41 A A 3.0 none 0.0 CB 2.0 90 50 1.80 75 .smallcircle. Comp-Ex. 42
B A 3.0 none 0.0 CB 2.0 90 50 1.80 76 .smallcircle. Comp-Ex. 43 C A
3.0 none 0.0 CB 2.0 90 50 1.80 74 .smallcircle. Comp-Ex. 44 A A 3.0
none 0.0 none 0 90 0 0.00 58 .smallcircle. Comp-Ex. 45 B A 3.0 none
0.0 none 0 90 0 0.00 62 .smallcircle. Comp-Ex. 46 C A 3.0 none 0.0
none 0 90 0 0.00 60 .smallcircle.
Lithium ion secondary batteries of Examples 1 to 38 were excellent
in the results of cycle characteristics and safety tests. On the
other hand, in Comparative Examples 1 to 40 using the positive
electrode containing no maleimide compound had a problem in the
results of the overcharge test. While comparative Examples 41 to 43
used positive electrodes containing only carbon black as a
conductive agent, the results showed that they were inferior in
cycle characteristics to a battery using carbon nanotubes as a
conductive agent. While comparative Examples 44 to 46 used positive
electrodes containing no conductive agent, the results showed that
they were further inferior in cycle characteristics to Comparative
Examples 41 to 43.
INDUSTRIAL APPLICABILITY
The battery according to the present invention can be utilized in,
for example, all the industrial fields requiring a power supply and
the industrial fields pertaining to the transportation, storage and
supply of electric energy. Specifically, it can be used in, for
example, power supplies for mobile equipment such as cellular
phones and notebook personal computers; power supplies for
moving/transporting media such as trains, satellites and submarines
including electrically driven vehicles such as an electric vehicle,
a hybrid vehicle, an electric motorbike, and an electric-assisted
bike; backup power supplies for UPSs; and electricity storage
facilities for storing electric power generated by photovoltaic
power generation, wind power generation and the like.
EXPLANATION OF REFERENCE
1 positive electrode active material layer 2 negative electrode
active material layer 3 positive electrode current collector 4
negative electrode current collector 5 separator 6 laminate package
7 negative electrode lead terminal 8 positive electrode lead
terminal 10 film package 20 battery element 25 separator 30
positive electrode 40 negative electrode
* * * * *